Autoimmune diseases are typically challenging to diagnose, and in general individuals with one autoimmune disease are at higher risk for developing others, such as systemic autoimmune rheumatic diseases (SARDs). The presence of anti-nuclear autoantibodies (ANAs) is considered to be a hallmark of SARDS, and this association has been known for some time. The American College of Rheumatology (ACR) recommends testing for ANAs by indirect immunofluorescence (IIF) assay using HEp-2 cells, as described in their position statement in 2009. This statement explained that HEp-2 cells are able to express 100-150 relevant auto-antigens for use in ANA antibody detection. Thus, immobilized and preserved monolayers of HEp2 cells are the most commonly used substrates in IIF detection of ANAs.
ANA detection using IIF assay can reveal a multitude of patterns such as homogeneous, fine granular, coarse granular, nucleolar, centromere, nuclear dots, pleomorphic, mitochondrial and a variety of cytoskeletal patterns. Patients can have one or more patterns in combination with varying intensity of reactivity for each pattern. These patterns are a result of specific autoantibody binding to nuclear and cytoplasmic antigens which include but are not necessarily limited to dsDNA, nucleosomes, histones, SS-A Ro52/Ro60, SS-B/La, Ku, Mi-2, RNPs (Ribonucleoproteins: U1SnRNP 68, U1SnRNP A, U1SnRNP C, U2SnRNPs etc,), Sc1-70, PM-Scl, Fibrillarin, Th/To, CENP-B, CENP-A, Sp100, PCNA, Ribo-P, Jol, AMA-M2, Actin, Vimentin, and others.
Other methodologies have been utilized for screening and confirmation of ANAs. However, due to a variety of reasons, which include but are not limited to prevalence of false negative and false positive results, lack of standardization of test algorithms (i.e., reflex testing), and an inability to detect the diverse arrays of ANAs prevalent in individuals with SARDS, use of HEp-2 cells as the substrate for ANA testing remains the gold standard. Unfortunately, use of HEp-2 cells also involves complex test interpretation, false results and specialized skills, in part because it has been reported that up to 20% of apparently healthy subjects give a positive ANA IIF test result due to the presence of autoantibodies that recognize the so-called “dense fine speckles 70” (DFS70) antigen, which is also referred to herein and in the art as lens epithelium-derived growth factor (LEDGF). PSIP1/LEDGF is also known as AA408851, AU015605, Dfs70, Ledgf, Ledgfa, Ledgfb, mLEDGF, PC4 and SFRS1-interacting protein (PSIP1), Psip2 (isoform), p52, p75, PAIP encoded by the PSIP1 gene. Moreover, the DFS IIF pattern has been reported in up to 20% of ANA positive healthy subjects, but often not in ANA positive sera obtain from SARD patients (Mahler and Fritzler 2012). Since the main objective of the ANA HEp-2 test is to function as a tool for diagnosing and classifying SARD, as well as potentially other autoimmune diseases, the anti-DFS70 antibodies and the DFS pattern they produce reduce the usefulness of the ANA test, such as by increasing false results and otherwise complicating test interpretation. This has important ramifications for a variety of approaches that rely on accurate detection of ANA and treatment decisions for patients who are tested for ANA antibodies. Thus, there is an ongoing and unmet need for improved compositions and methods for detecting ANA. The present disclosure meets these and other needs.